The present invention relates to membrane electrode assemblies for use in direct methanol fuel cells. The membrane electrode assemblies of the present invention comprise a polymer electrolyte membrane with cathode and anode layers having a low content of catalysts with cathode and anode layers on either side of the membrane. The membrane electrode assemblies are serigraphically printed on an electron conducting substrate such as graphite or carbon paper with an ink comprising catalyst loaded carbon and water dispersed polymer electrolyte membrane material dispersed in a mixture of water, propanol and methanol. Following printing, the anode and cathode layers are boiled in deionized water to remove impurities. The anode and cathode layers and the polymer electrolyte membrane are then placed in a constraint and axially or semi-isostatically compressed, preferably via heat, to form the membrane electrode assemblies.
Fuel cells are energy conversion devices being considered as a possible alternative to internal combustion engines. One type of fuel cell comprises a solid polymer electrolyte (SPE) membrane, such as a sulfonated fluorinated polymer membrane material like NAFION, which provides ion exchange between the cathode and anode electrodes. Various configurations of SPE fuel cells as well as methods for their preparation have been described. See e.g. U.S. Pat. Nos. 4,469,579; 4,826,554; 5,211,984; 5,272,017; 5,316,871; 5,399,184; 5,472,799; 5,474,857; and 5,702,755.
SPE fuel cells offer several advantages over liquid electrolyte fuel cells. These include greater power densities, lower operating temperatures, and longer operating lifetimes. In addition, SPE materials are generally resistant to corrosion and easy to incorporate into fuel cell structures. Accordingly, attempts have been made to utilize these various solid polymer electrolyte (SPE) fuel cells as an electronic power source for electric automobiles and space crafts.
However, the need for a catalyst such as platinum in the SPE fuel cells has made these cells more expensive than alternative energy sources.
The present invention provides a method for producing SPE fuel cells with lower catalyst content and enhanced electrochemical efficiency.
An object of the present invention is to provide a method for producing membrane electrode assemblies for use in direct methanol fuel cells which comprises serigraphically printing cathode and anode catalyst layers onto graphite or carbon paper; boiling the printed cathode and anode layers to remove impurities; placing a polymer electrolyte membrane between the cathode and anode layers and inserting them into a constraint which restricts their volume and lateral defamation; and semi-isostatically compressing the cathode and anode layers to the polymer electrolyte membrane.
Another object of the present invention is to provide a more electrochemically efficient membrane electrode assembly comprising a polymer electrolyte membrane and printed anode and cathode layer comprising a low content of catalysts located on either side of the polymer electrolyte membrane, wherein the printed anode and cathode layers were washed to remove impurities prior to assembly.